This invention relates to a method and a device for recording data on an optical disc by irradiating laser beam on a recording surface of an optical disc and, more particularly, to a method and device of this type which, in a case where a recording speed can be varied, is capable of preventing deterioration of quality in a recorded signal regardless of a selected recording speed.
As one of systems for recording data on a writable optical disc, there is a CD-WO (Compact Disc Write Once) system. In this system, a write once type recording is performed in accordance with the CD format. In this CD-WO system, a recording pit length of 3T to 11T (1T=1/4.3218 MHz=231 ns) is employed as recording data. If laser beam of a pulse width equivalent to length of a pit to be formed is irradiated, a pit actually formed becomes longer by about 1T than the object pit length due heating of the disc. Hence, so-called (n-1) strategy is adopted according to which, as shown in FIG. 2, recording laser beam is irradiated with a pulse width (n-1)T which is shorter by 1T than length of an object pit to be formed (e.g., a pulse width of 2T when an object pit of 3T is to be formed and a pulse width of 3T when an object pit of 4T is to be formed).
In recording data on an optical disc, it is convenient to provide a recording device with a function of recording data not only at a normal recording speed but also at a higher recording speed such as double speed, quadruple speed etc. which will shorten recording time. As a case of using a quadruple recording speed, there can be a case, for example, where data (e.g., CD-ROM data or digital audio data) to be recorded is stored in a hard disc, this data is read out in a quadruple compressed form and recorded on an optical disc by rotating the optical disc (CD-WO disc) at a quadruple recording speed. As a case of using a double recording speed, there can be a case, for example, where data is reproduced from a Compact Disc by rotating a Compact Disc player at a double speed and copying the data on an optical disc (CD-WO disc) by driving the optical disc at a double recording speed.
It has however been found as a result of experiments that, in a case where data is recorded at a higher recording speed than a normal recording speed with irradiation time of recording laser beam being always maintained at (n-1)T, there occurs increasing deterioration of quality in a recorded signal such as increase of crosstalk (i.e., leakage of a signal between adjacent tracks) as the recording speed becomes higher.
It is, therefore, an object of the invention to provide a method and a device for preventing deterioration of quality in a recorded signal regardless of the recording speed.